I wish to give ordinary users read/write access to /dev/ttyUSB* (so till software at a shop can control the till roll printer and open the till drawer).

It seems every release of CentOs changes how this should be done!In CentOs 5, I edited /etc/udev/rules.d/50-udev.rules. I understand in CentOs 6 the rules are now in /lib/udev/rules.d, but I can't find any reference to ttyUSB in that folder, other than:

This was more of an exploratory question - I am testing and debugging my install scripts on a VM, and I don't think I can attach the actual USB hardware to the VM (I don't have drivers for the host O/S).

However, I am burning a real CentOs 6 DVD as we speak, preparatory to installing it on a real box, so I'll let you know.

In the mean time, a pointer to documentation on how the CentOs 6 rules work would be nice?

Turns out I won't be able to answer your question for a while - CentOs 6 won't install on the old target hardware I have to hand (no pae or cx8, so I have to wait for the client to decide on and procure the new target hardware before I can actually check out the printer hardware.

nikkilocke wrote:This was more of an exploratory question - I am testing and debugging my install scripts on a VM, and I don't think I can attach the actual USB hardware to the VM (I don't have drivers for the host O/S).

Perhaps not relevant to CentOS, but it is a rare host OS that does not have native USB drivers. Many virtualization methods allow USB passthrough.

In the mean time, a pointer to documentation on how the CentOs 6 rules work would be nice?

Thanks for the pointer to the upstream docs. Is there no corresponding doc website for CentOs? (It might work a bit better - the search results page in the RedHat one is a total mess when viewed with Chrome.)

I have read that page, and the adjoining ones (which seem to be about Logical Volumne Management, which, AFAIK, is something to do with disks. I have copied the sample rules file from .usr/share/docs/device-mapper* into /lib/udev/rules.d

I am still totally baffled as to how to write a rule which will match /dev/ttyUSB*, and set the ownership and permissions.

What is a "DM device"?

Do I put in a rule like:

KERNEL=="ttyUSB*", GROUP="epos", MODE="0666"

or do the rules in this file have to begin with "ENV{DM"

Are the rules executed in filename alphanumeric order? If so, what happens if 2 rules match the same device?

Will the rule at the start of this fileENV{DM_UDEV_RULES_VSN}!="?*", GOTO="dm_end"

cause any rules I add later to be skipped?

Am I even using the right file?

Am I alone in wanting to read some documentation which tells me what to do, instead of fiddling about to find out what works?

If so, I answered as best I could in posts #3 and #4 - I am not in a position to run the command you suggest, because I am unable to install CentOs on the hardware I have here, and I am unable to attach the relevant device to the VM I am testing in.

I will have to wait until I have CentOs installed on hardware to which I can attach the printer before I can proceed further.